1. Field of the Invention
The present invention relates to a sealing apparatus disposed at a compartment inlet/outlet of an atmosphere facility, such as a bright annealing furnace, which performs heat treatment, such as annealing and strain relief annealing, for metal strips, such as stainless steel strips, other alloy steel strips, high-alloy strips, silicon steel strips, copper alloy strips and copper strips, without coloring or discoloring their surfaces or without generating oxide films on their surfaces.
2. Description of the Related Art
A combustible or flammable reducing atmospheric gas, such as an ammonia decomposition gas or a mixture gas of 75% of hydrogen gas and 25% of nitrogen gas, is supplied into a heat treatment furnace for annealing metal strips, such as stainless steel strips, or for strain relief annealing such metal strips to eliminate strain, without generating oxide films on their surfaces, and the pressure in the furnace is maintained about 10 to 50 mm H.sub.2 O higher than the outside air.
This kind of heat treatment furnace is provided with sealing apparatuses for shutting off a metal strip passing portion at the compartment inlet and the compartment outlet so as to prevent the above-mentioned combustible or flammable gas in the furnace from leaking.
FIG. 12 is a vertical sectional view showing a schematic representation of a bright annealing furnace 3 equipped with prior art sealing apparatuses 1, 2. A metal strip 4, such as a stainless steel strip, is heat treated so as to be annealed in a reducing atmosphere formed by a mixture gas of 75% of hydrogen gas and 25% of nitrogen gas, for example, in the furnace body 5 of the vertical bright annealing furnace 3, while the pressure in the furnace is maintained about 10 to 50 mm H.sub.2 O higher than the outside air. The metal strip 4 and the furnace body 5 are grounded electrically via a grounding line 6. The metal strip 4 is subjected to a surface cleaning treatment as a pretreatment before it is annealed by the bright annealing furnace 3. The direction of the metal strip 4 then changes due to a deflector roll 7 positioned at the furnace body entrance and the metal strip 4 enters the furnace body 5 from a compartment inlet 8. After the traveling direction of the metal strip 4 is reversed by a turn roll 9 in the furnace, the metal strip 4 is annealed and cooled, then delivered downward through compartment outlet 10. The direction of the metal strip 4 is changed by a deflector roll 11 at the exit and the metal strip 4 is taken up on a tension reel.
In this kind of bright annealing furnace 3, the metal strips 4, such as stainless steel strips, other alloy steel strips, high-alloy strips, copper alloy strips and copper strips, are annealed continuously while preventing oxidation. It is therefore very important to seal a furnace gas 5a at the compartment inlet 8 and the compartment outlet 10 while the metal strip 4 is passed through so as to ensure the quality of products and the safety of furnace operation. In order to provide the necessary sealing, the above-mentioned sealing apparatuses 1, 2 are provided.
FIG. 13 is a partial front view showing the structure of the sealing apparatus 2 disposed at the compartment outlet 10 shown in FIG. 12, and FIG. 14 is a side view of the sealing apparatus 2. This prior art is disclosed in Japanese Examined Patent Publication JP(B2) 42-18893 (1967), for example. Since the structure of the sealing apparatus 1 disposed at the compartment inlet 8 is similar to that of the sealing apparatus 2 disposed at the compartment outlet 10, the structure of the sealing apparatus 1 is not described here to avoid overlaps. In the above-mentioned sealing apparatus 2, a pair of elastic rotation rolls 16, the outer peripheral portions of which are made of an elastic material such as rubber, are pushed against the metal strip 4 and a pair of elastic pads 17 by the action force of a roll open/close device 18 so as to seal the boundary between each elastic rotation roll 16 and the metal strip 4 and the boundary between each elastic rotation roll 16 and each elastic pad 17.
The elastic pads 17 are secured to the surfaces of sealing fixtures 19 respectively, and each sealing fixture 19 is secured to the furnace body 5. In the roll open/close device 18, levers 20 are swivelably mounted on fixing pins 21 which are used as the rotation centers of the levers. A bearing 28 for supporting a roll shaft 22 of the elastic rotation roll 16 is disposed at one end of each lever 20. The other end of each lever 20 is connected to an end of a link member 23 via a pin 24. The other end of each link member 23 is connected to a piston rod 27 of a cylinder 26 via a pin 25.
As shown in FIG. 14, when the piston rod 27 is retracted, the elastic rotation rolls 16 are brought close to each other to sandwich the metal strip 4. Furthermore, the elastic rotation rolls 16 are pushed against the elastic pads 17. Consequently, sealing is performed at the contact position between each elastic rotation roll 16 and the metal strip 4 and at the contact position between each elastic rotation roll 16 and each elastic pad 17.
Both ends of each roll shaft 22 in the axial direction thereof are inserted into the cutouts 30 of side walls 29 secured to the furnace body 5 and rotatably supported around the axis of the roll shaft 22 by bearings 28 disposed at one end of each lever 20. On each roll shaft 22, a roll covering 31, the outer peripheral portion of which is made of an elastic material such as rubber as described above, is provided coaxially. Three washers 32, 33, 34 are interposed between one end face of the roll covering 31 in the axial direction thereof and the inner surface of one side wall 29 facing the end face, and are also interposed between the other end face of the roll covering 31 in the axial direction thereof and the inner surface of the other side wall 29 facing the other end face. Among the three washers 32 to 34, the washer 32 disposed closest to the end face of the roll covering 31 is made of expanded-sponge-like neoprene rubber. The central washer 33 contacting the washer 32 is made of fluororesin having a low coefficient of friction, such as polytetrafluoroethylene resin (PTFE). The washer 34 disposed nearest to the side wall 29 is made of carbon steel, stainless steel or non-ferrous metal.
As described above, the prior art disclosed in Japanese Examined Patent Publication JP(B2) 42-18893 (1967) uses three washers 32 to 34 to prevent each elastic rotation roll 16 from contacting the side wall 29 during passing of a metal strip and to seal the end faces of the rolls.
In this kind of prior art, the side walls 29 are disposed on both sides of each elastic rotation roll 16 in the axial direction thereof. The three washers 32 to 34 are interposed between the side wall 29 and the roll covering 31 on each side of the elastic rotation roll 16. In this prior art arrangement, in order to seal clearances between the side wall 29 and the end face of the elastic rotation roll 16 and the respective washers by an appropriate repulsion force generated by the washer 32, the washer 32 is required to be formed so as to have a thickness slightly larger than the dimension obtained by subtracting the thicknesses of the washers 33 and 34 from the clearance between the roll covering 31 and the side wall 29, taking into account of the shrinkage allowance of the washer 32. Furthermore, the elastic rotation roll 16 is required to be positioned and installed accurately so that the clearance between the end face of the roll covering 31 and the inner surface of the side wall 29 secured to the furnace body 5 on one side of the roll covering 31 is equal to the corresponding clearance on the other side of the roll covering 31. In case the clearance on one side or the clearances on both sides are more narrow than necessary at this time, a pushing force is applied to the side wall 29 by the repulsion force of the washer 32 and the rotation resistance of the elastic rotation roll 16 increases. Even when the elastic rotation roll 16 is positioned so as to have equal clearances on the right and left sides thereof, each of the elastic rotation rolls 16, sandwiching the metal strip 4, is always subjected to a thrust force in the axial direction due to a repulsion force caused by the snaking of the metal strip 4, because the metal strip 4 does not travel straight but slightly snakes repeatedly when the metal strip 4 is passed through the sealing apparatuses 1, 2 having the above-mentioned structure. In addition, the bearing 28 has play in the axial direction as a relief allowance for the thermal expansion of the roll shaft 22 so as to allow the elastic rotation roll 16 to move by a fraction of 1 mm. Therefore, the pushing force of the washer 32 against the secured side wall 29 changes at all times, and the rotation resistance also changes accordingly.
Furthermore, when the axial length of each elastic rotation roll 16 is changed because of thermal expansion, when the rubber washer 32 expands, shrinks, or changes in hardness or elastic force because of a temperature change, or when the washers 32 to 34 change in thickness because of partial wear, the pushing force against the roll covering 31 cannot be corrected to an appropriate value automatically, because the inner dimension between the side walls 29 of the sealing apparatus is determined and the axial position of the elastic rotation roll 16 is also determined. This causes the problem of being unable to offer a stable sealing effect for an extended period of time. Moreover, when one of the three washers 32 to 34 is required to be replaced because of deformation due to wear or heat generation or because of a change in rotation resistance due to attached abrasion powder or the like, the entire production line must be stopped and the elastic rotation roll 16 must be removed. In this way, the replacement of the washers 32 to 34 is troublesome.
Additionally, to adjust the pushing force against the roll covering 31 by the washers 32 to 34, the washers 32 to 34 must be replaced with those having different thicknesses. In the case of this kind of adjustment of the pushing force, since the elastic rotation roll 16 must be removed, a process line must be stopped, thereby causing the problem of reducing productivity.
Moreover, in the prior art arrangement, wear occurs at the metallic washer 34, which is pushed against the side wall 29, and the metallic roll shaft 22, which rotates, due to the metallic contact between the inner diameter portion of the washer 34 and the roll shaft. When the mutual contact pressure among the washers 32 to 34 is raised for increasing sealing performance, the sliding friction among the washers 32 to 34 increases, the rotation torque of the elastic rotation roll 16 is not completely isolated but is transmitted to the metallic washer 34, and wear occurs due to metallic contact between the washer 34 and the side wall 29, thereby causing the problem of reduced sealing performance due to attachment of dirt, caused by generated metal powder, to the metal strip 4, and due to damage or wear of the metal material for the side wall 29, the washer 34 and the roll shaft 22. To the contrary, when the contact pressure among the washers 32 to 34 is reduced, the above-mentioned friction can be reduced, thereby preventing the generation of metal powder and wear. However, the sealing performance is lowered. In this way, a conflicting problem occurs. In particular, when the metal strip 4 is passed through at high speed, the washers 32 to 34 tend to experience significant wear and they must be replaced frequently, thereby causing the problem of being unable to carry out stable operation for an extended period of time.
Furthermore, in case the covering 31 of the elastic rotation roll 16 is an insulator, static electricity is generated by the deformation or separation of the covering 31 due to continuous pushing and rotation during operation, or by repeated friction with the elastic pad 17. Since the atmospheric gas in the furnace leaks in the vicinities of the sealing apparatuses 1, 2, and the vicinities, having a dew point of about -50.degree. C. are very dry, the electrification potential amounts up to .+-.5000 V to 15000 V. Therefore, in case the static electricity causes sparks to adjacent metal parts, a fire may be caused easily or sometimes an explosion may occur.
Accordingly, the purpose of the present invention is to provide a sealing apparatus for a compartment inlet/outlet of an atmosphere facility, in which stable operation can be performed for an extended period of time. Also, the safety of operation is enhanced by preventing ignition due to sparks caused by static electricity, the installation position of each elastic rotation roll can be adjusted easily without removing the elastic rotation roll 16, that is, with the atmospheric gas remaining supplied, and each elastic rotation roll can be installed easily and accurately at the optimal position without requiring skills.